src/soc/decoder/power_svp64_prefix.py

   1 """SVP64 Prefix Decoder
   2
   3 """
   4
   5 from nmigen import Module, Elaboratable, Signal, Mux, Const, Cat
   6 from nmigen.cli import rtlil
   7 from nmutil.util import sel
   8
   9 from soc.consts import SVP64P
  10
  11 # SVP64 Prefix fields: see https://libre-soc.org/openpower/sv/svp64/
  12 # identifies if an instruction is a SVP64-encoded prefix, and extracts
  13 # the 24-bit SVP64 context (RM) if it is
  14 class SVP64PrefixDecoder(Elaboratable):
  15
  16     def __init__(self):
  17         self.opcode_in = Signal(32, reset_less=True)
  18         self.raw_opcode_in = Signal.like(self.opcode_in, reset_less=True)
  19         self.is_svp64_mode = Signal(1, reset_less=True)
  20         self.svp64_rm = Signal(24, reset_less=True)
  21         self.bigendian = Signal(reset_less=True)
  22
  23     def elaborate(self, platform):
  24         m = Module()
  25         opcode_in = self.opcode_in
  26         comb = m.d.comb
  27         # sigh copied this from TopPowerDecoder
  28         # raw opcode in assumed to be in LE order: byte-reverse it to get BE
  29         raw_le = self.raw_opcode_in
  30         l = []
  31         for i in range(0, 32, 8):
  32             l.append(raw_le[i:i+8])
  33         l.reverse()
  34         raw_be = Cat(*l)
  35         comb += opcode_in.eq(Mux(self.bigendian, raw_be, raw_le))
  36
  37         # start identifying if the incoming opcode is SVP64 prefix)
  38         major = sel(m, opcode_in, SVP64P.OPC)
  39         ident = sel(m, opcode_in, SVP64P.SVP64_7_9)
  40
  41         comb += self.is_svp64_mode.eq(
  42             (major == Const(1, 6)) &   # EXT01
  43             (ident == Const(0b11, 2))  # identifier bits
  44         )
  45
  46         with m.If(self.is_svp64_mode):
  47             # now grab the 24-bit ReMap context bits,
  48             rm = sel(m, opcode_in, SVP64P.RM)
  49             comb += self.svp64_rm.eq(rm)
  50
  51         return m
  52
  53     def ports(self):
  54         return [self.opcode_in, self.raw_opcode_in, self.is_svp64_mode,
  55                 self.svp64_rm, self.bigendian]
  56
  57
  58 if __name__ == '__main__':
  59     svp64 = SVP64PrefixDecoder()
  60     vl = rtlil.convert(svp64, ports=svp64.ports())
  61     with open("svp64_prefix_dec.il", "w") as f:
  62         f.write(vl)